Idiom: to choke
Sam: How did you do on your biology test this morning?
Todd: Oh man, I totally choked. I couldn't remember any of the information I studied last night. I can't believe it.
Sam: Really? That's too bad.
Chrissy: I have my first piano recital this Friday night. I'm getting so nervous.
Jane: Don't worry. You'll do fine. You practice a lot, right?
Chrissy: Yeah, I've been practicing for hours everyday, but I'm afraid I'll get really scared when I see the audience. What if I choke and mess up the whole piece of music?
Jane: Try to calm down. You'll be ok.
Meaning: To choke is an idiom that is used to describe someone who totally fails at a moment when they are expected or hoping to perform well.